HK2 Factory Implementation Singleton - jersey-2.0

Question

I am trying to understand HK2 Factory implementation in Jersey Application.
Goal : How to implement singleton factory?
// Below is the simple factory implementation
public class MyFactory implements Factory<SomeObject> {
private static final Logger logger = LoggerFactory.getLogger(MyFactory.class);
private final CloseableService closeService;
#Inject
public MyFactory(CloseableService closeService) {
this.closeService = closeService;
}
#Override
public MyFactory provide() {
logger.debug("provide object from MyFactory");
SomeObject objectFromFactory = new SomeObject();
this.closeService.add(() -> dispose(objectFromFactory));
return objectFromFactory;
}
#Override
public void dispose(SomeObject instance) {
// destroy instance
logger.debug("dispose object from MyFactory");
}
}
// and binding
bindFactory(MyFactory.class).to(SomeObject.class).in(Singelton.class);
// to check object creation and destruction
bind(HK2InstanceListener.class).to(InstanceLifecycleListener.class).in(Singleton.class);
// and injecting in some resource class
#Inject
SomeObject useThisObject;
//updated information
AbstractBinder abstractBinder = configureBinder();
ServiceLocator appServiceLocator = configureHK2(abstractBinder);
public static AbstractBinder configureBinder() {
return new AbstractBinder() {
#Override
protected void configure() {
bindFactory(MyFactory.class).to(SomeObject.class).in(Singelton.class);
// to check object creation and destruction
bind(HK2InstanceListener.class).to(InstanceLifecycleListener.class).in(Singleton.class);
}
}
public ServiceLocator configureHK2(AbstractBinder binder) {
ServiceLocatorFactory factory = ServiceLocatorFactory.getInstance();
ServiceLocator locator = factory.create("my-test-server");
DynamicConfigurationService dcs = locator.getService(DynamicConfigurationService.class);
DynamicConfiguration dc = dcs.createDynamicConfiguration();
locator.inject(binder);
binder.bind(dc);
dc.commit();
return locator;
}
On starting application I see below in the logs
10:38:34.122 [grizzly-http-server-0] DEBUG com.test.HK2InstanceListener - HK2 before object create : com.test.MyFactory
10:38:34.125 [grizzly-http-server-0] DEBUG com.test.HK2InstanceListener - HK2 before object create : com.test.MyFactory
10:38:34.125 [grizzly-http-server-0] DEBUG com.test.HK2InstanceListener - HK2 after object create : com.test.MyFactory
10:38:34.125 [grizzly-http-server-0] DEBUG com.test.MyFactory provide - object from MyFactory
10:38:35.700 [grizzly-http-server-0] DEBUG com.test.HK2InstanceListener - HK2 after object create : com.test.MyFactory
10:38:37.743 [grizzly-http-server-0] DEBUG com.test.MyFactory - dispose object from MyFactory
When scope = Singleton
creating two objects of MyFactory
Next request fails with null pointer exception #Inject.
When scope = RequestScoped, PerLookup
Every request creates two objects of MyFactory
By Singleton factory, I understand is, a single object of factory (MyFactory) which provides some kind of objects upon injection.
So (1) should work or am I missing something?
And Why two objects of Factory?
Any suggestions? Thanks in advance.
HK2 Version : 2.5.0-b60
Jersey Version: 2.26
Additional Information on NPE
It was not from HK2 but behavior differs between .in(Singleton.class) and .in(PerLookup.class)
// SomeObject looks like
Class SomeObject
{
private Stack<String> someStack;
public SomeObject() {
// this may be the issue for Singleton
this.someStack = new Stack();
}
public someOperation(String stackIt)
{
// NPE location
this.someStack.push(stackIt);
}
}
NPE at above location when below
bindFactory(MyFactory.class,Singleton.class).to(SomeObject.class).in(Singleton.class);
No NPE at above location when below
bindFactory(MyFactory.class,Singleton.class).to(SomeObject.class).in(PerLookup.class);

Answer 1

When you do your bindFactory use the second argument to bind the Factory as a Singleton. The way you are doing it only the provide method is bound as a Singleton. So to make the Factory itself also a Singleton do it like this:
bindFactory(MyFactory.class, Singleton.class).to(SomeObject.class).in(Singelton.class);
That should get both the thing provided AND the Factory itself bound as singletons.